1. Field of the Invention
The present invention relates to a method and to a device for detecting an anomaly in the formation of the shed in a Jacquard-type weaving loom. The invention also concerns a weaving loom equipped with such a device.
2. Brief Description of the Related Art
FR-A-2 772 796 for example discloses using an electrical actuator for controlling the displacement of the harness cords of a Jacquard loom harness.
Furthermore, it is known to equip a Jacquard-type weaving loom with a so-called xe2x80x9cwarp stop motionxe2x80x9d device which comprises metallic drop wires supported by each of the warp yarns of the loom and conducting bars extending over the width of the loom. In the event of rupture of a warp yam, the drop wire that it supports comes, under the effect of its own weight, into contact with conducting bars, which creates an electrical contact between these conducting bars which are made alive. Such contact can be detected by an electrical monitoring system, which makes it possible to interrupt the operation of the loom immediately and to draw an operator""s attention, for example with the aid of a telltale lamp. However, such a warp stop motion device presents considerable limitations. Firstly, once the loom is stopped, the operator must seek which warp yam is effectively broken, which involves manually displacing the drop wires in order to identify the one which is creating the contact. This operation may be long and requires qualified manpower. In addition, the positioning of the metallic drop wires on the different warp yams, sometimes called xe2x80x9cthreadingxe2x80x9d, is a long and expensive operation. The cost of the equipment used for effecting the warp stop motion is non negligible, since it must include one drop wire for each warp yarn, i.e. for example up to more than 10,000 drop wires, and conducting bars having to be incorporated in the structure of the loom and supplied with voltage. Moreover, the known warp stop motion devices are sensitive to pollution due to the flock which is most often produced during the weaving operations. It is therefore necessary to provide periodic cleaning operations for this device.
It is a more particular object of the present invention to overcome these drawbacks by proposing a novel method for detecting an anomaly which does not require resorting to a conventional warp stop motion device and allows reliable and rapid detection and identification of a broken warp yarn, a damaged elastic return element, or a broken harness cord or one disconnected from the corresponding heddle.
To that end, the invention relates to a method for detecting an anomaly in the formation of the shed in a Jacquard-type weaving loom comprising electrical actuators for displacing the heddles controlling the position of the warp yarns of the loom. This method consists in:
determining a so-called xe2x80x9cnormal effortxe2x80x9d or xe2x80x9cnormal weaving effortxe2x80x9d, exerted by at least one actuator on at least one harness cord in order to displace, between two positions of its normal stroke, at least one heddle connected to a normally taut warp yarn;
determining, from this normal effort, at least one threshold value representative of a limit of a range of values of normal weaving effort;
determining, while the loom is in operation, a so-called xe2x80x9coperational effortxe2x80x9d exerted by this actuator on this harness cord;
comparing at least one value representative of this operational effort with the threshold value, and
generating a first, so-called xe2x80x9canomaly signalxe2x80x9d when the value representative of the operational effort is outside the range defined by the threshold value.
The method of the invention takes advantage of the fact that it is possible to determine the efforts exerted by an electrical actuator without resorting to ancillary mechanical devices, while the operations of memorization, comparison and logic processing may be carried out in an electronic controller used, furthermore, for controlling the actuators. The method of the invention dispenses with the operation of threading of the warp stop motion drop wires, this allowing an appreciable saving of time and consequently reducing the operating costs of the loom. In addition, the method allows a rapid and precise identification of the position of a warp yarn at the level of which the shed does not conform to the desired weave, whether it be due to a rupture of this yarn, to a dysfunction of the elastic return means or to a defect in the kinematic link between the actuator and the heddle, as the actuator for which an anomaly signal is generated is immediately located.
According to advantageous but non-compulsory aspects of the invention, the method incorporates one or more of the following characteristics:
It further consists in determining a so-called xe2x80x9cno load effortxe2x80x9d, exerted by the actuator on at least one harness cord in order to displace a heddle not influenced by a warp yarn between two positions of its normal stroke; in memorizing, for this actuator, values representative of this no load effort; in comparing, when an anomaly signal has been generated, the value representative of the afore-mentioned operational effort with the memorized values representative of the no load effort, and in generating a second, so-called xe2x80x9cwarp yarn rupture signalxe2x80x9d when the representative values compared are substantially identical. The method of the invention therefore makes it possible not only to detect an anomaly in the formation of the shed but to detect the cause thereof, namely the rupture of a warp yarn, when it can be established that the effort exerted by the actuator is substantially equal to the effort that it exerts in the absence of a warp yarn.
It further consists in determining a so-called xe2x80x9cunloaded effortxe2x80x9d exerted by the actuator on at least one harness cord in order to displace, between two positions of its stroke, a heddle connected to a warp yarn which is normally taut but disconnected from the elastic return means; in memorizing, for this actuator, values representative of this unloaded effort; in comparing, when the anomaly signal has been generated, the value representative of the operational effort with the memorized values representative of the unloaded effort, and in generating a third, so-called xe2x80x9celastic return means rupture signalxe2x80x9d when the representative values in question are substantially identical. According to this aspect of the invention, the method makes it possible to identify the rupture or unhooking of a return spring of a heddle associated with a warp yarn, which guides the operator in the repair to be carried out.
It consists in generating a fourth, so-called xe2x80x9cconnection rupture signalxe2x80x9d when the value representative of the operational effort is substantially zero. In effect, when the effort generated by the actuator is zero, this means that it is no longer kinematically connected to the heddle which is in that case no longer driven.
It consists in activating the actuator for which an anomaly signal has been generated so as to render distinctive the or each heddle driven by this actuator. This aspect of the invention takes advantage of the fact that it is certain that the actuator for which an anomaly has been detected is located by the controller of the Jacquard mechanism, this then allowing the operator to locate the anomaly more readily. It may be provided to displace the or each heddle driven by the actuator in question towards a position visibly offset with respect to that of the other heddles, for example a top position of its stroke, while the other heddles are displaced towards a bottom position of their stroke. It may also be provided to impart an oscillating movement to the or each heddle driven by the actuator in question, while the other heddles are immobilized. In any case, the operator immediately locates the warp yarn or yarns on which his verifications are to be concentrated.
It consists in determining the afore-mentioned efforts by measuring at least one electrical supply parameter of the actuator.
It consists in repeatedly determining, memorizing and comparing the afore-mentioned efforts for each actuator of the loom during operation thereof. This systematic nature guarantees the efficiency of the surveillance envisaged.
It consists in determining the value of the effort exerted by a warp yarn on a heddle and in generating an anomaly signal when the value of this effort is substantially different from a reference value.
The method of the invention therefore allows the rapid detection of an anomaly of the shed, its treatment, particularly by stopping the loom, and the localization of this anomaly, particularly by locating the actuator concerned. According to variant embodiments of the method, it even allows the type of anomaly encountered to be identified.
The invention also relates to a device for carrying out the method described hereinbefore, and, more specifically, to a device comprising:
means for determining at least one reference effort exerted by at least one actuator on at least one harness cord in order to displace at least one heddle between two positions of its stroke, under predetermined conditions;
a memory adapted to store values characteristic of this reference effort;
means for determining a so-called xe2x80x9coperational effortxe2x80x9d exerted by the actuator on the harness cord when the loom is in operation;
means for comparing values characteristic of the operational effort and threshold values established from the memorized values characteristic of the reference effort, and
a logic unit adapted to identify an abnormal value of the operational effort thanks to the results furnished by the comparison means.
The reference effort may be the normal effort identified hereinabove, but may equally well be the xe2x80x9cno loadxe2x80x9d and xe2x80x9cunloadedxe2x80x9d efforts for which the means of determination used are identical.
According to an advantageous aspect of the invention, the device comprises means for displaying the reference and/or the position of the or each heddle driven by an actuator for which the logic unit has detected an abnormal value. These means may include an indicator which the operator consults in order to know on which part of the loom he must intervene.
Finally, the invention relates to a Jacquard type weaving loom equipped with a device as described hereinbefore. Such a loom is more economical than the looms equipped with conventional warp stop motion devices, while it is easier to use for an operator and it does not require tedious threading operations. In addition, such a loom may allow automatized repairs when an anomaly is observed, as the device and the method of the invention allow a precise identification of the cause of an anomaly and its physical location on the loom.